A 42-year-old woman from Delhi with a history of pulmonary tuberculosis treated 5 years ago now presents with hemoptysis and dyspnea. High-resolution CT chest shows a cavitary lesion in the right upper lobe with a mobile intracavitary mass. Sputum culture grows Aspergillus fumigatus. Histopathology of the cavitary lesion shows remnants of caseous material, fibrosis, and fungal hyphae. Which of the following best explains the pathogenesis of this complication?

Explanation

## Aspergilloma (Mycetoma) in Tuberculosis **Key Point:** An aspergilloma is a fungal ball (mycelial mass) that colonizes a pre-existing cavity, most commonly a healed or chronic TB cavity. It is a **non-invasive colonization**, not true invasive aspergillosis. ### Pathogenesis of Aspergilloma 1. **Pre-existing cavity** from TB (or other chronic lung disease: bronchiectasis, cystic fibrosis, sarcoidosis) 2. **Loss of local immunity** in the fibrotic, avascular cavity 3. **Aspergillus spores** inhaled and germinate in the cavity 4. **Mycelial growth** within the cavity without tissue invasion 5. **Fungal ball** composed of hyphae, fibrin, and cellular debris ### Distinguishing Features | Feature | Aspergilloma | Invasive Aspergillosis | Chronic Cavitary TB | |---------|--------------|----------------------|---------------------| | **Cavity origin** | Pre-existing (TB, old infarct) | None initially | Active TB infection | | **Tissue invasion** | No (non-invasive) | Yes (angioinvasive) | Yes (granulomatous) | | **Immune status** | Immunocompetent or mild impairment | Severely immunocompromised | Variable | | **Histology** | Fungal hyphae in cavity lumen | Hyphae invading lung parenchyma | Caseating granuloma | | **Hemoptysis** | Common (cavity wall erosion) | Rare | Variable | | **Culture** | Aspergillus from sputum | Blood culture positive | Mycobacterium from sputum | **High-Yield:** The **intracavitary mobile mass** on imaging ("halo sign" or "air crescent sign") is pathognomonic for aspergilloma. The fungal ball moves with patient position. **Mnemonic:** **CAVITY** = **C**hronic **A**spergillus **V**ascular **I**nvasion **T**issue **Y**es (invasive) vs. **NO** (aspergilloma) ### Pathological Findings in Aspergilloma ```mermaid flowchart TD A[Healed TB cavity with fibrosis]:::outcome --> B[Avascular, immunologically privileged space]:::outcome B --> C[Aspergillus spore inhalation]:::action C --> D{Local immunity intact?}:::decision D -->|Yes| E[Spore clearance]:::outcome D -->|No| F[Spore germination and hyphal growth]:::action F --> G[Aspergilloma formation]:::outcome G --> H[Cavity wall erosion by fungal proteases]:::action H --> I[Hemoptysis and hemorrhage]:::urgent ``` **Clinical Pearl:** Aspergillomas are often asymptomatic and discovered incidentally on imaging. However, they can cause life-threatening hemoptysis due to erosion of cavity walls and adjacent blood vessels (bronchial arteries). ### Why TB Cavities Are Susceptible - **Fibrotic, avascular tissue** with poor blood supply - **Acidic microenvironment** (pH 5–6) favors Aspergillus growth - **Impaired local cell-mediated immunity** in chronic TB - **High oxygen tension** in cavities (Aspergillus is aerobic) [cite:Robbins 10e Ch 8; Harrison 21e Ch 197]